Electrically variable transmission with selective fixed ratio operation

ABSTRACT

An electrically variable transmission includes: an input member to receive power from an engine; an output member; first and second motor/generators; and first and second differentially geared planetary gear sets each having first, second and third gear members. The input member is continuously connected to the first member of the first planetary gear set, and the output member is continuously connected to the first member of the second planetary gear set. The first motor/generator is continuously connected to the second member of the first planetary gear set, and selectively connected to the second member of the second planetary gear set. The second motor/generator is continuously connected with the third member of the second planetary gear set. Five or six torque transfer devices selectively connect members of the planetary gear sets with each other or with ground. The torque transfer devices are engageable in combinations of two or three to provide five or six available fixed speed ratios.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application60/606,359, filed Sep. 1, 2004, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present invention relates to electrically variable transmissionswith selective operation both in power-split variable speed ratio rangesand in up to six fixed speed ratios.

BACKGROUND OF THE INVENTION

Internal combustion engines, particularly those of the reciprocatingpiston type, currently propel most vehicles. Such engines are relativelyefficient, compact, lightweight, and inexpensive mechanisms by which toconvert highly concentrated energy in the form of fuel into usefulmechanical power. A novel transmission system, which can be used withinternal combustion engines and which can reduce fuel consumption andthe emissions of pollutants, may be of great benefit to the public.

The wide variation in the demands that vehicles typically place oninternal combustion engines increases fuel consumption and emissionsbeyond the ideal case for such engines. Typically, a vehicle ispropelled by such an engine, which is started from a cold state by asmall electric motor and relatively small electric storage batteries,then quickly placed under the loads from propulsion and accessoryequipment. Such an engine is also operated through a wide range ofspeeds and a wide range of loads and typically at an average ofapproximately a fifth of its maximum power.

A vehicle transmission typically delivers mechanical power from anengine to the remainder of a drive system, such as fixed final drivegearing, axles and wheels. A typical mechanical transmission allows somefreedom in engine operation, usually through alternate selection of fiveor six different drive ratios, a neutral selection that allows theengine to operate accessories with the vehicle stationary, and clutchesor a torque converter for smooth transitions between driving ratios andto start the vehicle from rest with the engine turning. Transmissiongear selection typically allows power from the engine to be delivered tothe rest of the drive system with a ratio of torque multiplication andspeed reduction, with a ratio of torque reduction and speedmultiplication known as overdrive, or with a reverse ratio.

An electric generator can transform mechanical power from the engineinto electrical power, and an electric motor can transform that electricpower back into mechanical power at different torques and speeds for theremainder of the vehicle drive system. This arrangement allows acontinuous variation in the ratio of torque and speed between the engineand the remainder of the drive system, within the limits of the electricmachinery. An electric storage battery used as a source of power forpropulsion may be added to this arrangement, forming a series hybridelectric drive system.

The series hybrid system allows the engine to operate with someindependence from the torque, speed and power required to propel avehicle, so the engine may be controlled for improved emissions andefficiency. This system allows the electric machine attached to theengine to act as a motor to start the engine. This system also allowsthe electric machine attached to the remainder of the drive train to actas a generator, recovering energy from slowing the vehicle into thebattery by regenerative braking. A series electric drive suffers fromthe weight and cost of sufficient electric machinery to transform all ofthe engine power from mechanical to electrical in the generator and fromelectrical to mechanical in the drive motor, and from the useful energylost in these conversions.

A power-split transmission can use what is commonly understood to be“differential gearing” to achieve a continuously variable torque andspeed ratio between input and output. An electrically variabletransmission can use differential gearing to send a fraction of itstransmitted power through a pair of electric motor/generators. Theremainder of its power flows through another, parallel path that is allmechanical and direct, of fixed ratio, or alternatively selectable.

One form of differential gearing, as is well known to those skilled inthis art, may constitute a planetary gear set. Planetary gearing isusually the preferred embodiment employed in differentially gearedinventions, with the advantages of compactness and different torque andspeed ratios among all members of the planetary gear set. However, it ispossible to construct this invention without planetary gears, as byusing bevel gears or other gears in an arrangement where the rotationalspeed of at least one element of a gear set is always a weighted averageof speeds of two other elements.

A hybrid electric vehicle transmission system also includes one or moreelectric energy storage devices. The typical device is a chemicalelectric storage battery, but capacitive or mechanical devices, such asan electrically driven flywheel, may also be included. Electric energystorage allows the mechanical output power from the transmission systemto the vehicle to vary from the mechanical input power from the engineto the transmission system. The battery or other device also allows forengine starting with the transmission system and for regenerativevehicle braking.

An electrically variable transmission in a vehicle can simply transmitmechanical power from an engine input to a final drive output. To do so,the electric power produced by one motor/generator balances theelectrical losses and the electric power consumed by the othermotor/generator. A hybrid electrically variable transmission system in avehicle includes an electrical storage battery, so the electric powergenerated by one motor/generator can be greater than or less than theelectric power consumed by the other. Electric power from the batterycan sometimes allow both motor/generators to act as motors, especiallyto assist the engine with vehicle acceleration. Both motors cansometimes act as generators to recharge the battery, especially inregenerative vehicle braking.

A successful substitute for the series hybrid transmission is thetwo-range, input-split and compound-split electrically variabletransmission now produced for transit buses. Such a transmissionutilizes an input means to receive power from the vehicle engine and apower output means to deliver power to drive the vehicle. First andsecond motor/generators are connected to an energy storage device, suchas a battery, so that the energy storage device can accept power from,and supply power to, the first and second motor/generators. A controlunit regulates power flow among the energy storage device and themotor/generators as well as between the first and secondmotor/generators.

Operation in first or second variable-speed-ratio modes of operation maybe selectively achieved by using clutches in the nature of first andsecond torque transfer devices. In the first mode, an input-power-splitspeed ratio range is formed by the application of the first clutch, andthe output speed of the transmission is proportional to the speed of onemotor/generator. In the second mode, a compound-power-split speed ratiorange is formed by the application of the second clutch, and the outputspeed of the transmission is not proportional to the speeds of either ofthe motor/generators, but is an algebraic linear combination of thespeeds of the two motor/generators. Operation at a fixed transmissionspeed ratio may be selectively achieved by the application of both ofthe clutches. Operation of the transmission in a neutral mode may beselectively achieved by releasing both clutches, decoupling the engineand both electric motor/generators from the transmission output.

The two-range, input-split and compound-split electrically variabletransmission may be constructed with two sets of planetary gearing orwith three sets of planetary gearing. In addition, some embodiments mayutilize three torque transfer devices—two to select the operational modedesired of the transmission and the third selectively to disconnect thetransmission from the engine. In other embodiments, all three torquetransfer devices may be utilized to select the desired operational mode.

U.S. Pat. No. 6,527,658, issued Mar. 4, 2003 to Holmes et al andcommonly assigned with the present application, discloses anelectrically variable transmission utilizing two planetary gear sets,two motor/generators and two clutches to provide input split, compoundsplit, neutral and reverse modes of operation. Both planetary gear setsmay be simple, or one may be individually compounded. An electricalcontrol member regulates power flow among an energy storage device andthe two motor/generators. This transmission provides two ranges or modesof electrically variable transmission (EVT) operation, selectivelyproviding an input-power-split speed ratio range and acompound-power-split speed ratio range. One fixed speed ratio can alsobe selectively achieved.

SUMMARY OF THE INVENTION

The present invention improves upon the above-referenced prior arttransmissions by providing additional clutches to enhance operation ofthe transmission, to allow additional fixed speed ratios and to allow anadditional compound-power-split speed ratio range. An object of theinvention is to provide the best possible energy efficiency andemissions for a given engine. In addition, optimal performance,capacity, package size, and ratio coverage for the transmission aresought.

A fixed speed ratio is an operating condition in which the mechanicalpower input to the transmission is transmitted mechanically to output,and no power flow is necessary through the motor/generators. Anelectrically variable transmission that may selectively achieve severalfixed speed ratios for operation near full engine power can be smallerand lighter for a given maximum capacity. Fixed ratio operation may alsoresult in lower fuel consumption when operating under conditions whereengine speed can approach its optimum without using themotor/generators.

In comparison to prior art electrically variable transmissions with onlyone clutch for each of two speed ranges (C1 and C2), this inventionreduces power flow through the electrical path, reducing electricalcomponent costs and power losses. By providing a third clutch (C3), oneof the motors can thereby be locked to the transmission case to provide,along with the application of C2, an additional fixed speed ratio toallow high speed cruising with improved transmission efficiency.

A fourth clutch (C4) may be provided as a “lock-up clutch” or“direct-drive clutch” to lock the elements of one of the planetary gearsets together. This clutch allows the transmission to transmit torqueand power at two additional fixed speed ratios: a low ratio with C1 andC4 engaged and speed reduction through the other planetary gear set; anda direct drive ratio with C2 and C4 engaged. The action of the C4 clutchallows more torque and power to be transmitted by the transmission inthese fixed ratios than at similar ratios by action of themotor/generators and C1 or C2 clutch alone. The C4 clutch enablesmaximum power to be achieved for passing or towing and hauling heavyloads in a truck or similar vehicle. The C4 enables the use of smallerelectrical components with high-power engines, a combination which maybe practical for personal trucks.

An extra fourth clutch (C4B) may be added to provide six fixed ratios.

Additionally, a fifth clutch (C5) may be added to decouple themechanical path from the engine to the output, and to allow theelectrical path to be engaged alone. Sudden and unpredicted changes ininput speed, such as from starting and stopping the engine, can then bemade without disturbing the output. The C5 clutch enables onemotor/generator to drive the vehicle forward or in reverse whiledecoupled from the other motor/generator and the engine. When using theengine to drive the vehicle in reverse in the input-split range, anadverse torque reaction occurs, so the release of the C5 clutch improvesthe continuous reverse grade ability of the vehicle.

One aspect of the present invention provides a new and novelelectrically variable transmission, as above, that is significantly lesscomplex than prior known electrically variable transmissions.

It is a further aspect of the present invention to provide a new andnovel electrically variable transmission, as above, that can bemanufactured at a significant cost reduction relative to prior knownelectrically variable transmissions. The present invention may achievethis through the use of additional clutches to provide up to six fixedspeed ratios and therefore allow smaller electrical components, and theuse of only two planetary gear sets, the minimum for a compound powersplit.

These and other aspects of the invention, as well as the advantagesthereof over existing and prior art forms, which will be apparent inview of the following detailed specification, are accomplished by meanshereinafter described and claimed.

By way of a general introductory description, an electrically variabletransmission embodying the concepts of the present invention has aninput member to receive power from an engine and an output member todeliver power to the drive members that propel the vehicle. There arefirst and second motor/generators as well as first and second planetarygear sets. Each planetary gear set has an inner gear member and an outergear member that meshingly engage a plurality of planet gear membersrotatably mounted on a carrier. The input member is continuouslyconnected to one member of the first planetary gear set, and the outputmember is continuously connected to one member of the second planetarygear set. One motor/generator is continuously connected to anothermember in the first planetary gear set as well as being selectivelyconnected to a member of the second planetary gear set. The secondmotor/generator is continuously connected to the remaining member of thesecond planetary gear set, and is continuously connected to theremaining member of the first planetary gear set. Alternately, thesecond motor/generator may be selectively connected to the remainingmember of the first planetary gear set.

A first torque transfer device (C1) selectively grounds one member ofthe second planetary gear set, and a second torque transfer device (C2)selectively connects this same member of the second planetary gear setto the inner gear member of the first planetary gear set as well as tothe rotor of one motor/generator.

An optional third torque transfer device (C3) selectively connects saidremaining members of the first and second planetary gear sets and thesecond motor/generator to ground. Alternatively, the optional thirdtorque transfer device (C3) may selectively connect said remainingmember of the first planetary gear set to ground.

An optional fourth torque transfer device (C4) selectively connects atleast two members of the transmission together such that the members ofthe first planetary gear set rotate together at the same speed. Theoptional fourth torque transfer device (C4) may selectively connect amember of the first planetary gear subset to another member of the firstplanetary gear subset. Alternatively, the optional fourth torquetransfer device (C4) may selectively connect said remaining members ofthe first and second planetary gear sets and the second motor/generatorto the member of the first planetary gear set that is connected with theinput member. In one embodiment, both of the above-mentioned fourthtorque transfer devices are implemented (C4A and C4B).

An optional fifth torque transfer device (C5) selectively disconnectssaid remaining member of the first planetary gear set from both theremaining member of the second planetary gear set and the secondelectric motor/generator. Accordingly, the remaining member of the firstplanetary gear set may be selectively or continuously connected to boththe remaining member of the second planetary gear set and the secondelectric motor/generator, depending on whether the C5 clutch is presentor not.

Another aspect of the invention provides an electrically variabletransmission including: an input member to receive power from an engine;an output member; first and second motor/generators; and first andsecond differentially geared planetary gear sets each having first,second and third gear members. The input member is continuouslyconnected to the first member of the first planetary gear set, and theoutput member is continuously connected to the first member of thesecond planetary gear set. The first motor/generator is continuouslyconnected to the second member of the first planetary gear set, andselectively connected to the second member of the second planetary gearset. The second motor/generator is continuously connected with the thirdmember of the second planetary gear set. A first torque transfer deviceselectively grounds the second member of the second planetary gear set.A second torque transfer device selectively connects the second memberof the second planetary gear set to the second member of the firstplanetary gear set. A third torque transfer device selectively groundsthe third member of the first planetary gear set. A fourth torquetransfer device selectively connects the first or second member of thefirst planetary gear set with the third member of the second planetarygear set. A fifth torque transfer device selectively connects the thirdmember of the first planetary gear set with the third member of thesecond planetary gear set. The torque transfer devices are engageable incombinations of two or three to provide five or six available fixedspeed ratios.

The first, second and third members of the planetary gear sets maycomprise a ring gear, sun gear, and carrier, in any order. Preferably,the first, second and third members of the first planetary gear setcomprise a ring gear, sun gear and carrier, respectively, and the first,second and third members of the second planetary gear set comprise acarrier, ring gear and sun gear respectively.

The torque transfer devices are selectively engaged to provide,sequentially, an input-split mode, a compound-split mode, and anoutput-split mode, as output speed of the transmission increases. Thissequence is most desirable because it minimizes power loops.

Each power split mode has a ratio range of power-feed-forward operationand one or more ratio ranges of power-loop operation. Inpower-feed-forward operation, which is desired, the power in theelectric motor/generators flows in the direction from input to output inparallel with the power flow through the gearing from input to output.In power-loop operation, which is undesirable, the power in the electricmotor/generators flows in the direction from output to input, such thata power loop is formed and the power flow through the gearing is greaterthan the input power or the output power.

An input-split range of speed ratios is most useful for low outputspeeds, relative to the input speed, because the input-split range haspower-feed-forward operation from zero output speed up to some ratio,then power-loop operation at higher output speeds. An output-split rangeof operation is most useful for high output speeds, relative to theinput speed, because the output-split range has power-loop operationbelow some ratio, then power-feed-forward operation at higher outputspeeds.

The above features and advantages, and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic stick diagram representing an electricallyvariable transmission implemented in a front wheel drive transmission,wherein four torque transfer devices are implemented to provide fourfixed ratios;

FIG. 2 is a chart illustrating clutching engagements and motor/generatoroperation for different operating conditions of the transmission of FIG.1;

FIG. 3 is a schematic stick diagram representing another form of anelectrically variable transmission in a rear wheel drive transmission,wherein four torque transfer devices are implemented to provide fourfixed ratios;

FIG. 4 is a schematic stick diagram representing one preferred form ofan electrically variable transmission embodying the concepts of thepresent invention in a rear wheel drive transmission, wherein fivetorque transfer devices are implemented to provide five or six fixedratios;

FIG. 5 is a chart illustrating clutching engagements for differentoperating conditions of the transmission of FIG. 4, providing sixavailable fixed speed ratios;

FIG. 6 is a schematic stick diagram representing another embodiment ofthe invention, providing another three-range input-compound-output splitelectrically variable transmission with five fixed speed ratios;

FIG. 7 is a chart illustrating clutching engagements for differentoperating conditions of the transmission of FIG. 6, providing five fixedspeed ratios;

FIG. 8 is a schematic stick diagram representing another embodiment ofthe invention, providing a three-range input-compound-output splitelectrically variable transmission with six single-transition fixedspeed ratios; and

FIG. 9 is a chart illustrating clutching engagements for differentoperating conditions of the transmission of FIG. 8, providing six fixedspeed ratios.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

U.S. Pat. No. 6,527,658, issued Mar. 4, 2003 to Holmes et al and herebyincorporated by reference in its entirety, discloses an electricallyvariable transmission utilizing two planetary gear sets, twomotor/generators and two clutches to provide input split, compoundsplit, neutral and reverse modes of operation. The present inventionprovides a relatively similar structure with three or four additionalclutches to potentially improve performance.

Description of Related EVT Configurations Having 4 Fixed Ratios

With particular reference, initially, to FIG. 1, an electricallyvariable transmission is designated generally by the numeral 10. Thetransmission 10 is designed to receive at least a portion of its drivingpower from an engine 12. As shown, the engine 12 has an output shaft 14that may also serve as the forward input member of a transient torquedamper 16, which includes an input clutch 17. Transient torque dampersare well known in this art, but irrespective of the particular transienttorque damper 16 employed, the output member thereof serves as the inputmember 18 of the transmission 10, as will be hereinafter more fullydescribed.

In the embodiment depicted the engine 12 may be a fossil fuel engine,such as a diesel engine which is readily adapted to provide itsavailable power output typically delivered at a constant number ofrevolutions per minute (RPM).

Irrespective of the means by which the engine 12 is connected to thetransmission input member 18, the transmission input member 18 isoperatively connected to a planetary gear set 20 in the transmission 10.

The transmission 10 utilizes two differential gear sets, preferably inthe nature of planetary gear sets. The first planetary gear set 20employs an outer gear member 22, typically designated as the ring gear.The ring gear 22 circumscribes an inner gear member 24, typicallydesignated as the sun gear. A carrier 26 rotatably supports a pluralityof planet gears 28, 29 such that each planet gear 28 meshingly engagesthe outer, ring gear member 22 and each planet gear 29 meshingly engagesthe inner, sun gear member 24 of the first planetary gear set 20. Theinput member 18 is secured to the ring gear member 22 of the firstplanetary gear set 20.

The second planetary gear set 32 also has an outer gear member 34, oftenalso designated as the ring gear, that circumscribes an inner gearmember 36, also often designated as the sun gear. A plurality of planetgears 38 are also rotatably mounted in a carrier 40 such that eachplanet gear member 38 simultaneously, and meshingly, engages both theouter, ring gear member 34 and the inner, sun gear member 36 of thesecond planetary gear set 32.

The planetary gear set 20 is compound, and the planetary gear set 32 issimple. The inner, sun gear 36 of the second planetary gear set 32 isconjoined, as through a central shaft 42, to the carrier 26 of the firstplanetary gear set 20.

The first preferred embodiment 10 also incorporates first and secondmotor/generators 46 and 48, respectively. The stator 50 of the firstmotor/generator 46 is secured to the generally annular, interior surface52 of the transmission housing 54. The rotor 56 of the firstmotor/generator 46 is secured to a sleeve shaft 58. The inner, sun gear24 of the first planetary gear set 20 secured to the forward end of thesleeve shaft 58, and the opposite end of the sleeve shaft 58 terminatesin a radially extending flange plate 60 which constitutes an interfacewith a clutch means, which is hereinafter described.

The stator 66 of the second motor/generator 48 is also secured to thegenerally annular, interior surface 52 of the transmission housing 54.The rotor 68 of the second motor/generator 48 is secured to the centralshaft 42, and as such the first and second planetary gear sets 20 and 32are further compounded.

The two planetary gear sets 20 and 32 as well as the twomotor/generators 46 and 48 may be coaxially oriented, as about theaxially disposed central shaft 42. This configuration assures that theoverall envelope—i.e., the circumferential dimension—of the transmission10 may be minimized.

The ring gear 34 of the second planetary gear set 32 is selectivelygrounded to the housing 54, as by a first clutch means in the nature ofa torque transfer device 62 (C1). That is, the grounded ring gear 34 isselectively secured against rotation by an operative connection to thenon-rotatable housing 54. The ring gear 34 of the second planetary gearset 32 is also selectively connected to the radially extending flangeplate 60, as by a second clutch means in the nature of a torque transferdevice 64 (C2). The first and second torque transfer devices 62 and 64are employed to assist in the selection of the operational modes of thehybrid transmission 10, as will be hereinafter more fully explained.

A third torque transfer device 65 (C3) selectively connects the carrier26, sun gear 36 and rotor 68 to the transmission housing 54.Accordingly, this torque-transfer device allows the secondmotor/generator 48 to be locked to the transmission housing whichprovides an additional available fixed ratio when the torque transferdevice 64 (C2) is also engaged.

A fourth torque transfer device 67 (C4) is provided as a “lock-up”clutch to lock the ring gear member 22 to the carrier 26. This torquetransfer device allows the transmission to transmit torque and power attwo additional fixed speed ratios: a low ratio with torque transferdevices 62 (C1) and 67 (C4) engaged, and a direct drive ratio withtorque transfer devices 64 (C2) and 67 (C4) engaged. This allows moretorque and power to be transmitted by the transmission in these fixedratios than at similar ratios by action of the C1 or C2 clutches andmotor/generators alone. The lock-up clutch enables maximum power to beachieved quickly for passing, towing and hauling in a personal truck orthe like, while providing four available fixed ratios and operating withat least one mechanical point in the first mode and at least twomechanical points in the second mode—i.e., three mechanical points, oneat each of three separate vehicle speeds.

The output drive member 70 of the transmission 10 is secured to thecarrier 40 of the second planetary gear set 32. The output drive member70 may present peripheral gear teeth (not shown) meshingly to engage agear (not shown) presented from a transfer case (not shown) that mayfunction as a differential to two corresponding drive shafts.Preferably, this configuration is used in a front wheel drive vehicle.It should also be appreciated that the output drive member 70 couldtransfer output power to the transfer case by a chain drive or other,similar mechanical connection.

Returning now to the description of the power sources, it should beapparent from the foregoing description, and with particular referenceto FIG. 1, that the transmission 10 selectively receives power from theengine 12. As will now be explained, the hybrid transmission alsoreceives power from an electric power source 82. The electric powersource 82 may be one or more batteries. Other electric power sources,such as fuel cells, that have the ability to provide, or store, anddispense electric power may be used in place of batteries withoutaltering the concepts of the present invention. As was explained inconjunction with the description of the engine 12 and themotor/generators 46 and 48, it must be similarly understood that thehorsepower output of the electrical power source is also not critical tothe invention.

The electric power source 82 communicates with an electrical controlunit (ECU) 84 by electrical transfer conductors 86A and 86B. The ECU 84communicates with the first motor/generator 46 by electrical transferconductors 86C and 86D, and the ECU 84 similarly communicates with thesecond motor/generator 48 by electrical transfer conductors 86E and 86F.

As apparent from the previous paragraph, a particular structural member,component or arrangement may be employed at more than one location. Whenreferring generally to that type of structural member, component orarrangement, a common numerical designation is employed. However, whenone of the structural members, components or arrangements so identifiedis to be individually identified, it will be referenced by virtue of aletter suffix employed in combination with the numerical designationemployed for general identification of that structural member, componentor arrangement. Thus, there are six electrical transfer conductors thatare generally identified by the numeral 86, but the specific,individual, electrical transfer conductors are, therefore, identified as86A, 86B, 86C, 86D, 86E and 86F in the specification and on thedrawings. This same suffix convention shall be employed throughout thespecification.

General Operating Considerations

One of the primary control devices is a well known drive range selector(not shown) that directs a conventional electronic control unit (the ECU84) to configure the transmission for either the park, reverse, neutral,or forward drive range. The second and third primary control devicesconstitute an accelerator pedal (not shown) and a brake pedal (also notshown). The information obtained by the ECU from these three primarycontrol sources is designated as the “operator demand.” The ECU alsoobtains information from a plurality of sensors (input as well asoutput) as to the status of: the torque transfer devices (either appliedor released); the engine output torque; the unified battery, orbatteries, capacity level; and, the temperatures of selected vehicularcomponents. The ECU determines what is required and then manipulates theselectively operated components of, or associated with, the transmissionappropriately to respond to the operator demand.

Both simple and compound planetary gear sets are used. In a simpleplanetary gear set a single set of planet gears are normally supportedfor rotation on a carrier that is itself rotatable.

In a simple planetary gear set, when the sun gear is held stationary andpower is applied to the ring gear of a simple planetary gear set, theplanet gears rotate in response to the power applied to the ring gearand thus “walk” circumferentially about the fixed sun gear to effectrotation of the carrier in the same direction as the direction in whichthe ring gear is being rotated.

When any two members of a simple planetary gear set rotate in the samedirection and at the same speed, the third member is forced to turn atthe same speed, and in the same direction. For example, when the sungear and the ring gear rotate in the same direction, and at the samespeed, the planet gears do not rotate about their own axes but ratheract as wedges to lock the entire unit together to effect what is knownas direct drive. That is, the carrier rotates with the sun and ringgears.

However, when the two gear members rotate in the same direction, but atdifferent speeds, the direction in which the third gear member rotatesmay often be determined simply by visual analysis, but in manysituations the direction will not be obvious and can only be accuratelydetermined by knowing the number of teeth present on all the gearmembers of the planetary gear set.

Whenever the carrier is restrained from spinning freely, and power isapplied to either the sun gear or the ring gear, the planet gear membersact as idlers. In that way, the driven member is rotated in the oppositedirection as the drive member. Thus, in many transmission arrangementswhen the reverse drive range is selected, a torque transfer deviceserving as a brake is actuated frictionally to engage the carrier andthereby restrain it against rotation so that power applied to the sungear will turn the ring gear in the opposite direction. Thus, if thering gear is operatively connected to the drive wheels of a vehicle,such an arrangement is capable of reversing the rotational direction ofthe drive wheels, and thereby reversing the direction of the vehicleitself.

In a simple set of planetary gears, if any two rotational speeds of thesun gear, the planet carrier, and the ring gear are known, then thespeed of the third member can be determined using a simple rule. Therotational speed of the carrier is always proportional to the speeds ofthe sun and the ring, weighted by their respective numbers of teeth. Forexample, a ring gear may have twice as many teeth as the sun gear in thesame set. The speed of the carrier is then the sum of two-thirds thespeed of the ring gear and one-third the speed of the sun gear. If oneof these three members rotates in an opposite direction, the arithmeticsign is negative for the speed of that member in mathematicalcalculations.

The torque on the sun gear, the carrier, and the ring gear can also besimply related to one another if this is done without consideration ofthe masses of the gears, the acceleration of the gears, or frictionwithin the gear set, all of which have a relatively minor influence in awell-designed transmission. The torque applied to the sun gear of asimple planetary gear set must balance the torque applied to the ringgear, in proportion to the number of teeth on each of these gears. Forexample, the torque applied to a ring gear with twice as many teeth asthe sun gear in that set must be twice that applied to the sun gear, andmust be applied in the same direction. The torque applied to the carriermust be equal in magnitude and opposite in direction to the sum of thetorque on the sun gear and the torque on the ring gear.

In a compound planetary gear set, the utilization of inner and outersets of planet gears effects an exchange in the roles of the ring gearand the planet carrier in comparison to a simple planetary gear set. Forinstance, if the sun gear is held stationary, the planet carrier willrotate in the same direction as the ring gear, but the planet carrierwith inner and outer sets of planet gears will travel faster than thering gear, rather than slower.

In a compound planetary gear set having meshing inner and outer sets ofplanet gears the speed of the ring gear is proportional to the speeds ofthe sun gear and the planet carrier, weighted by the number of teeth onthe sun gear and the number of teeth filled by the planet gears,respectively. For example, the difference between the ring and the sunfilled by the planet gears might be twice as many teeth as are on thesun gear in the same set. In that situation the speed of the ring gearwould be the sum of two-thirds the speed of the carrier and one thirdthe speed of the sun. If the sun gear or the planet carrier rotates inan opposite direction, the arithmetic sign is negative for that speed inmathematical calculations.

If the sun gear were to be held stationary, then a carrier with innerand outer sets of planet gears will turn in the same direction as therotating ring gear of that set. On the other hand, if the sun gear wereto be held stationary and the carrier were to be driven, then planetgears in the inner set that engage the sun gear roll, or “walk,” alongthe sun gear, turning in the same direction that the carrier isrotating. Pinion gears in the outer set that mesh with pinion gears inthe inner set will turn in the opposite direction, thus forcing ameshing ring gear in the opposite direction, but only with respect tothe planet gears with which the ring gear is meshingly engaged. Theplanet gears in the outer set are being carried along in the directionof the carrier. The effect of the rotation of the pinion gears in theouter set on their own axis and the greater effect of the orbital motionof the planet gears in the outer set due to the motion of the carrierare combined, so the ring rotates in the same direction as the carrier,but not as fast as the carrier.

If the carrier in such a compound planetary gear set were to be heldstationary and the sun gear were to be rotated, then the ring gear willrotate with less speed and in the same direction as the sun gear. If thering gear of a simple planetary gear set is held stationary and the sungear is rotated, then the carrier supporting a single set of planetgears will rotate with less speed and in the same direction as the sungear. Thus, one can readily observe the exchange in roles between thecarrier and the ring gear that is caused by the use of inner and outersets of planet gears which mesh with one another, in comparison with theusage of a single set of planet gears in a simple planetary gear set.

The normal action of an electrically variable transmission is totransmit mechanical power from the input to the output. As part of thistransmission action, one of its two motor/generators acts as a generatorof electrical power. The other motor/generator acts as a motor and usesthat electrical power. As the speed of the output increases from zero toa high speed, the two motor/generators gradually exchange roles asgenerator and motor, and may do so more than once. These exchanges takeplace around mechanical points, where essentially all of the power frominput to output is transmitted mechanically and no substantial power istransmitted electrically.

In a hybrid electrically variable transmission system, an electricstorage battery may also supply power to the transmission or thetransmission may supply power to the battery. If the battery issupplying substantial electric power to the transmission, such as forvehicle acceleration, then both motor/generators may act as motors. Ifthe transmission is supplying electric power to the battery, such as forregenerative braking, both motor/generators may act as generators. Verynear the mechanical points of operation, both motor/generators may alsoact as generators with small electrical power outputs, because of theelectrical losses in the system.

Contrary to the normal action of the transmission, the transmission mayactually be used to transmit mechanical power from the output to theinput. This may be done in a vehicle to supplement the vehicle brakesand to enhance or to supplement regenerative braking of the vehicle,especially on long downward grades. If the power flow through thetransmission is reversed in this way, the roles of the motor/generatorswill then be reversed from those in normal action.

Operation of FIG. 1 EVT

FIG. 2 is a chart illustrating clutching engagements for the torquetransfer devices 62, 64, 65 and 67, and motor/generator operation forthe motor/generators 46, 48 under different operating conditions of thetransmission 10 shown in FIG. 1.

In Mode 1 Reverse, the torque transfer device 62 is engaged and theengine 12 may hold the ring gear member 22 (in electric only drive), andthe second motor/generator 48 drives sun gear member 36, which rotatesthe carrier 40 to drive the output 70, while the first motor/generator46 is driven via the sun gear member 24 and carrier 26 with the sun gearheld stationary by the engine 12. Accordingly, the motor/generator 48drives in a reverse direction, and the motor/generator 46 is driven. Theengine 12 may or may not be running in reverse.

Accordingly, as described above, if the vehicle operator selects reverseoperation, the torque transfer device 62 is engaged to ground the outerring gear 34 of the second planetary gear set 32 to the housing 54. Infurther response to operator demand, the ECU 84 reverses the polarity ofthe electrical power being fed to the stator 66 of the secondmotor/generator 48. The resultant rotation of the rotor 68 inmotor/generator 48 then reverses from the rotational directionassociated with forward propulsion in the first, or input split, mode ofoperation. Under these conditions the inner, sun gear 36 of the secondplanetary gear set 32 drives the carrier 40 in planetary set 32 againstthe grounded outer, ring gear 34 to effect retro-rotation of the carrier40 and the output drive member 70 relative to the rotation of thosemembers during forward propulsion. Operation in the reverse mode is thusachieved.

In Mode 1 Forward, the same conditions apply as in Mode 1 Reversedescribed above, except the motor/generator is electrically actuated inan opposite rotational direction than in Mode 1 Reverse.

In Gear 1, the first fixed ratio is achieved by engaging the torquetransfer devices 62 and 67 while no power is transmitted through themotor/generators 46, 48.

In electrically variable Mode 1, the torque transfer device 62 isengaged and an input split mode is achieved because power enters thefirst planetary gear set at the ring gear member 22, and is splitbetween a mechanical path to the output 70 via carrier 26, sun gearmember 36 and carrier 40, and an electrical path via sun gear 24,motor/generator 46, motor/generator 48, sun gear member 36 and carrier40. Motor/generator 46 is driven by sun gear member 24, andmotor/generator 46 assists motor/generator 48 which is in drive mode(i.e., it acts as a motor). As such, the transmission 10 uses the ringgear 22 of the first planetary gear set 20 to receive power provided bythe engine 12 and carrier 26 of that same planetary gear set to providepower to the central shaft 42 by motor/generator 48 operating as amotor. Simultaneously, the transmission 10 uses the second planetarygear set 32 to multiply the torque received through the sun gear 36 ofthe second planetary gear set 32 and applied to the carrier 40 againstthe reaction imposed by the grounded ring gear 34 to be delivered tooutput drive member 70.

In electrically variable Mode 2, only torque transfer device 64 isengaged, and compound split operation is achieved. The motor/generator46 is in drive mode, and the motor/generator 48 is driven. In thecompound split mode the transmission uses the same two planetary gearsets 20 and 32 to provide gearing among the input member 18, bothmotor/generators 46 and 48 and the output drive member 70 so that powerflow is split into mechanical and electrical paths at both the input andthe output of the transmission.

In Gear 2, the second fixed ratio is achieved by engaging torquetransfer devices 62 and 64 while no power is transmitted through themotor/generators 46, 48.

In Gear 3, the third fixed ratio is achieved, which is a 1:1 directdrive ratio, by engaging torque transfer devices 64 and 67 while nopower is transmitted through the motor/generators 46, 48.

In Gear 4, the fourth fixed ratio is achieved by engaging torquetransfer devices 64 and 65 while no power is transmitted through themotor/generators 46, 48.

There is also a neutral mode, wherein the input member 18 from theengine 12 and the two motor/generators 46 and 48 are effectivelydisconnected from the output drive member 70 by allowing one member ofthe second planetary gear set 32 to spin freely. That is, both torquetransfer devices 62 and 64 are disengaged, thus allowing the outer gearmember 34 of the second planetary gear set 32 to spin freely and therebyeffect the neutral mode.

Description of FIG. 3 EVT

With particular reference to FIG. 3, another related electricallyvariable transmission is identified generally by the designation 110.The operating components of FIG. 3 are substantially similar to those ofFIG. 1, so like reference numerals are used to refer to like componentsfrom FIGS. 1 and 3. In FIG. 3, the transmission of FIG. 1 has beenrearranged in a rear wheel drive layout. It includes four torquetransfer devices, as in FIG. 1, and operates in accordance with thechart of FIG. 2.

The transmission 110 of FIG. 4 may, in part, receive its input powerfrom an engine 112. In the embodiment depicted the engine 112 may alsobe a fossil fuel engine, such as a diesel engine which is readilyadapted to provide its available power output typically delivered at aconstant number of revolutions per minute (RPM). As shown, the engine112 has an output shaft 114 that may also serve as the forward inputmember of a transient torque damper 116, which includes an input clutch117. The output member of the transient torsion damper 116 serves as theinput member 118 of the transmission 110.

Irrespective of the means by which the engine 112 is connected to thetransmission input member 118, the transmission input member 118 isoperatively connected to a planetary gear set 120 in the transmission110.

The transmission 110 utilizes two planetary gear sets. The first is acompound planetary gear set 120 that also employs an outer gear member122, typically designated as the ring gear. The ring gear 122 alsocircumscribes an inner gear member 124, typically designated as the sungear. The carrier assembly 126, in the planetary gear set 120, however,rotatably supports two sets of planet gears 128 and 129. Each of theplurality of planet gears 129 simultaneously, and meshingly, engages theinner, sun gear 124. Each planet gear 129 meshingly engages one, andonly one, adjacent planet gear 128. Each planet gear 128 simultaneously,and meshingly, engages the outer, ring gear member 122. Each planet gear128, in turn, meshingly engages one, and only one, adjacent planet gear129.

The input member 118 is secured to the ring gear member 122 of thecompound planetary gear set 120.

The second planetary gear set 132 is a simple planetary gear set, and ithas an outer gear member 134, often also designated as the ring gear,that circumscribes an inner gear member 136, also often designated asthe sun gear. As is typical in a simple planetary gear set, a pluralityof planet gears 138 are also rotatably mounted in a carrier 140 suchthat each planet gear member 138 simultaneously, and meshingly, engagesboth the outer, ring gear member 134 and the inner, sun gear member 136of the second planetary gear set 132, but the pinion gear members 138 donot engage each other.

In addition, the first and second planetary gear sets 120 and 132 aremutually compounded in that the inner, sun gear 136 of the secondplanetary gear set 132 is conjoined, as through a central shaft 142, tothe carrier assembly 126 of the compound planetary gear set 120. Thatis, the forward end of the central shaft 142 terminates in a radiallyextending flange portion 144 that is secured to the carrier assembly 126of the compound planetary gear set 120.

The second preferred embodiment 110 also incorporates first and secondmotor/generators 146 and 148, respectively. The stator 150 of the firstmotor/generator 146 is secured to the generally annular, interiorsurface 152 of the transmission housing 154. The rotor 156 of the firstmotor/generator 146 is secured to a sleeve shaft 158. The inner, sungear 124 of the first planetary gear set 120 is also secured to thesleeve shaft 158.

The ring gear 134 of the second planetary gear set 132 may beselectively grounded to the housing 154, as by a first torque transferdevice 162 (C1). That is, the grounded ring gear 134 is selectivelysecured against rotation by an operative connection to the non-rotatablehousing 154. The ring gear 134 of the second planetary gear set 132 isalso selectively connected to the radially extending flange plate 160,as by a second torque transfer device 164 (C2). The first and secondtorque transfer devices 162 and 164 are employed to assist in theselection of the operational modes of the hybrid transmission 110.

The carrier 126 is selectively grounded to the transmission housing viathe torque transfer device 165 (C3). Also, the carrier 126 isselectively connected to the ring gear member 122 via the torquetransfer device 167 (C4).

The stator 166 of the second motor/generator 148 is also secured to thegenerally annular, interior surface 152 of the transmission housing 154.The rotor 168 of the second motor/generator 148 is secured to thecarrier 126 of the compound planetary gear set 120.

The two planetary gear sets 120 and 132 as well as the twomotor/generators 146 and 148 may be coaxially oriented, as about theaxially disposed central shaft 142 and the input member 118. Thisconfiguration assures that the overall envelope—i.e., thecircumferential dimension—of the transmission 110 may be minimized.

The output drive member 170 of the transmission 110 is secured to thecarrier 140 of the second planetary gear set 132.

The electric power source 182 communicates with an electrical controlunit (ECU) 184 by electrical transfer conductors 186A and 186B. The ECU184 communicates with the first motor/generator 146 by electricaltransfer conductors 186C and 186D, and the ECU 184 similarlycommunicates with the second motor/generator 148 by electrical transferconductors 186E and 186F.

The operation of the transmission 110 is identical to that describedabove for transmission 10 with reference to FIG. 2.

Description of Preferred Embodiments of the Invention

Turning to FIG. 4, a transmission 210 is shown in accordance with apreferred embodiment of the invention. This transmission is functionallyand structurally similar to the transmissions 10 and 110 of FIGS. 1 and3, except that a fifth clutch is added. The fifth clutch (C5) enablesthe input and output to be disconnected for improved reversegrade-ability and smooth engine starting and stopping. The fifth clutchalso enables an output power split mode (EVT mode) and provides five orsix fixed ratios (one of which may be impractical).

As shown, the transmission 210 includes an input member 218 whichreceives power from the engine 212 and delivers the power to the firstplanetary gear set 220 via the ring gear member 222.

The transmission 210 utilizes two planetary gear sets. The first is acompound planetary gear set 220 that employs the outer gear member 222,typically designated as the ring gear. The ring gear 222 alsocircumscribes an inner gear member 224, typically designated as the sungear. The carrier assembly 226, in the planetary gear set 220, however,rotatably supports two sets of planet gears 228 and 229. Each of theplurality of planet gears 229 simultaneously, and meshingly, engages theinner, sun gear 224. Each planet gear 229 meshingly engages one, andonly one, adjacent planet gear 228. Each planet gear 228 simultaneously,and meshingly, engages the outer, ring gear member 222. Each planet gear228, in turn, meshingly engages one, and only one, adjacent planet gear229.

The second planetary gear set 232 is a simple planetary gear set, and ithas an outer gear member 234, often also designated as the ring gear,that circumscribes an inner gear member 236, also often designated asthe sun gear. As is typical in a simple planetary gear set, a pluralityof planet gears 238 are also rotatably mounted in a carrier 240 suchthat each planet gear member 238 simultaneously, and meshingly, engagesboth the outer, ring gear member 234 and the inner, sun gear member 236of the second planetary gear set 232, but the pinion gear members 238 donot engage each other.

The transmission 210 also incorporates first and second motor/generators246 and 248, respectively. The stator 250 of the first motor/generator246 is secured to the generally annular, interior surface 252 of thetransmission housing 254. The rotor 256 of the first motor/generator 246is secured to the inner, sun gear 224 of the first planetary gear set220.

The ring gear 234 of the second planetary gear set 232 may beselectively grounded to the housing 254, as by a first torque transferdevice 262 (C1). That is, the grounded ring gear 234 is selectivelysecured against rotation by an operative connection to the non-rotatablehousing 254. The ring gear 234 of the second planetary gear set 232 isalso selectively connected to the sun gear member 224, as by a secondtorque transfer device 264 (C2). The first and second torque transferdevices 262 and 264 are employed to assist in the selection of theoperational modes of the hybrid transmission 210.

The carrier 226 is selectively grounded to the transmission housing viathe torque transfer device 265 (C3). Also, the sun gear member 224 isselectively connected to the sun gear member 236 via the torque transferdevice 267 (C4).

A fifth torque transfer device 269 (C5) selectively connects the carrier226 with the sun gear member 236.

The stator 266 of the second motor/generator 248 is also secured to thegenerally annular, interior surface 252 of the transmission housing 254.The rotor 268 of the second motor/generator 248 is secured to the sungear member 236 of the planetary gear set 232.

The two planetary gear sets 220 and 232 as well as the twomotor/generators 246 and 248 may be coaxially oriented, as about theaxially disposed central shaft 242. This configuration assures that theoverall envelope—i.e., the circumferential dimension—of the transmission210 may be minimized.

The output drive member 270 of the transmission 210 is secured to thecarrier 240 of the second planetary gear set 232.

The chart of FIG. 5 illustrates clutching engagements for differentoperating conditions of the transmission of FIG. 4. For example, inelectric only mode (E1), the clutches 262 and 267 are engaged. Bothmotors can work to drive the vehicle forward or backwards to the limitof their combined torque and power and the battery limits, without aninput or lockup clutch. In electric only mode (E2) the clutches 264 and267 are engaged.

In series hybrid mode (S1), the clutches 262 and 265 are engaged (aftera clutch-to-clutch shift between clutches 267 and 265), and power fromthe engine is routed through the first planetary gear set 220, into tofirst motor/generator 246, into the second motor/generator 248, throughthe second planetary gear set 232, to the output 270. The series hybridmode (S1) may be used for engine starting and stopping.

In variable ratio mode (V1), clutches 262 and 269 are engaged to provideelectrically variable ratios in an input split mode (after a shiftbetween clutches 265 and 269).

A first fixed ratio is achieved in fixed gear (F1) with clutches 262,267 and 269 engaged. A second fixed ratio is achieved in fixed gear (F2)with clutches 262, 264 and 269 engaged. A third fixed ratio (F3) isachieved with clutches 262, 265 and 267 engaged. The fourth fixed ratio(F4) is achieved with clutches 264, 267 and 269 engaged. The fifth fixedratio (F5) is achieved with clutches 264, 265 and 269. The sixth fixedratio is achieved with the engagement of the clutches 264, 265 and 267.

In variable ratio mode (V2), clutches 264 and 269 are engaged to provideelectrically variable ratios in a compound split mode.

An output split range (V3) is provided with electrically variable ratioswhen clutches 264 and 265 are engaged, wherein the first motor/generator246 is geared at a fixed ratio to the input and the secondmotor/generator 248 provides speed ratio adjustments on the secondplanetary gear set 232. This output split range is achieved by turningclutch 269 off, which allows engine speed to fall without a power loop,making high overdrive more efficient. It may be practical to go fromthis output split range to the series hybrid mode with a synchronousclutch-to-clutch shift for coastdown.

The foregoing invention provides continuously variable ratio of inputspeed to output speed such that it can be effectively utilized as anautomotive transmission as well as a public transportation vehicle thatis subjected to a wide variety of operating requirements. The enginespeed can remain constant or vary independently of the vehicle speed.Shift to the selected mode of operation can be synchronous withoutwasted energy, so that the shifts can be instantaneous, imperceptibleand without wear to the transmission components.

Description of Second Preferred Embodiment

In yet another embodiment, the transmission 210 of FIG. 4 could bemodified by eliminating the clutch 265 (C3), and relocating the clutch267 (C4) so that it selectively connects the rotor 256 with the carrier226, while still providing input split, compound split and output splitmodes of operation. In this configuration, series hybrid operation (S1)is achieved with the engagement of clutches 262 (C1) and 267(C4).Variable ratio mode operation (V1) is achieved with the engagement ofclutches 262 (C1) and 269(C5). A first fixed ratio is achieved in fixedgear (F1) with clutches 262, 267 and 269 engaged. A second fixed ratiois achieved in fixed gear (F2) with clutches 262, 264 and 269 engaged. Athird fixed ratio is achieved in fixed gear (F3) with clutches 264, 267and 269 engaged. In variable ratio mode (V2), clutches 264 and 269 areengaged to provide electrically variable ratios in a compound splitmode. An output split range (V3) is provided with electrically variableratios when clutches 264 and 267 are engaged.

Description of Third Preferred Embodiment

Turning to FIG. 6, a transmission 310 is shown in accordance withanother preferred embodiment of the invention. This transmission isfunctionally and structurally similar to the transmission 210 of FIG. 4,except that the clutch 267 of FIG. 4 has been relocated.

As shown, the transmission 310 includes an input member 318 whichreceives power from the engine 312 and delivers the power to the firstplanetary gear set 320 via the ring gear member 322.

The transmission 310 utilizes two planetary gear sets. The first is acompound planetary gear set 320 that employs the outer gear member 322,typically designated as the ring gear. The ring gear 322 alsocircumscribes an inner gear member 324, typically designated as the sungear. The carrier assembly 326, in the planetary gear set 320, however,rotatably supports two sets of planet gears 328 and 329. Each of theplurality of planet gears 329 simultaneously, and meshingly, engages theinner, sun gear 324. Each planet gear 329 meshingly engages one, andonly one, adjacent planet gear 328. Each planet gear 328 simultaneously,and meshingly, engages the outer, ring gear member 322. Each planet gear328, in turn, meshingly engages one, and only one, adjacent planet gear329.

The second planetary gear set 332 is a simple planetary gear set, and ithas an outer gear member 334, often also designated as the ring gear,that circumscribes an inner gear member 336, also often designated asthe sun gear. As is typical in a simple planetary gear set, a pluralityof planet gears 338 are also rotatably mounted in a carrier 340 suchthat each planet gear member 338 simultaneously, and meshingly, engagesboth the outer, ring gear member 334 and the inner, sun gear member 336of the second planetary gear set 332, but the pinion gear members 338 donot engage each other.

The transmission 310 also incorporates first and second motor/generators346 and 348, respectively. The stator 350 of the first motor/generator246 is secured to the generally annular, interior surface 252 of thetransmission housing 354. The rotor 356 of the first motor/generator 346is secured to the inner, sun gear 324 of the first planetary gear set320.

The ring gear 334 of the second planetary gear set 332 may beselectively grounded to the housing 354, as by a first torque transferdevice 362 (C1). That is, the grounded ring gear 334 is selectivelysecured against rotation by an operative connection to the non-rotatablehousing 354. The ring gear 334 of the second planetary gear set 332 isalso selectively connected to the sun gear member 324, as by a secondtorque transfer device 364 (C2).

The carrier 326 is selectively grounded to the transmission housing viathe torque transfer device 365 (C3). Also, the sun gear member 336 isselectively connected to the ring gear member 322 via the torquetransfer device 367 (C4).

A fifth torque transfer device 369 (C5) selectively connects the carrier326 with the sun gear member 336.

The torque transfer devices 362, 364, 365, 367 and 369 are preferablyall dog clutches.

The stator 366 of the second motor/generator 348 is also secured to thegenerally annular, interior surface 352 of the transmission housing 354.The rotor 368 of the second motor/generator 348 is secured to the sungear member 336 of the planetary gear set 332.

The two planetary gear sets 320 and 332 as well as the twomotor/generators 346 and 348 may be coaxially oriented, as about theaxially disposed central shaft 342. This configuration assures that theoverall envelope—i.e., the circumferential dimension—of the transmission310 may be minimized.

The output drive member 370 of the transmission 310 is secured to thecarrier 340 of the second planetary gear set 332.

The chart of FIG. 7 illustrates clutching engagements for differentoperating conditions of the transmission of FIG. 6. These torquetransfer device engagements are similar to those described above withreference to FIG. 5, except the fixed ratio engagements have changed andthe ratios E1, E2 and F6 have been removed.

As shown in FIG. 7, a first fixed ratio is achieved in fixed gear (F1)with clutches 362, 367 and 369 engaged. A second fixed ratio is achievedin fixed gear (F2) with clutches 362, 364 and 369 engaged. A third fixedratio (F3) is achieved with clutches 364, 367 and 369 engaged. Thefourth fixed ratio (F4) is achieved with clutches 364, 365 and 369engaged. The fifth fixed ratio (F5) is achieved with clutches 364, 365and 367.

The rest of the operating modes are the same as those described abovewith reference to FIG. 5. The third EVT range (V3), an output-split toprange, allows the input-split and compound split ranges to becompressed, limiting the amount of power used by the electricmotor/generators 346, 348 without using fixed ratio operation. The fixedratio operation provides improved fuel economy, especially in F4 and F5(overdrive). Series operation is provided for reverse and for enginestarting and stopping. Either C3 (365) or C5 (369) would be normallyengaged to allow cold starting.

Description of Fourth Preferred Embodiment

Turning to FIG. 8, a transmission 410 is shown in accordance withanother preferred embodiment of the invention. This transmission isfunctionally and structurally similar to the transmission 310 of FIG. 6,except that the clutch 469 has been added.

As shown, the transmission 410 includes an input member 418 whichreceives power from the engine 412 and delivers the power to the firstplanetary gear set 420 via the ring gear member 422.

The transmission 410 utilizes two planetary gear sets. The first is acompound planetary gear set 420 that employs the outer gear member 422,typically designated as the ring gear. The ring gear 422 alsocircumscribes an inner gear member 424, typically designated as the sungear. The carrier assembly 426, in the planetary gear set 420, however,rotatably supports two sets of planet gears 328 and 329. Each of theplurality of planet gears 429 simultaneously, and meshingly, engages theinner, sun gear 324. Each planet gear 329 meshingly engages one, andonly one, adjacent planet gear 428. Each planet gear 428 simultaneously,and meshingly, engages the outer, ring gear member 422. Each planet gear428, in turn, meshingly engages one, and only one, adjacent planet gear429.

The second planetary gear set 432 is a simple planetary gear set, and ithas an outer gear member 434, often also designated as the ring gear,that circumscribes an inner gear member 436, also often designated asthe sun gear. As is typical in a simple planetary gear set, a pluralityof planet gears 438 are also rotatably mounted in a carrier 440 suchthat each planet gear member 438 simultaneously, and meshingly, engagesboth the outer, ring gear member 434 and the inner, sun gear member 436of the second planetary gear set 432, but the pinion gear members 438 donot engage each other.

The transmission 410 also incorporates first and second motor/generators446 and 448, respectively. The stator 450 of the first motor/generator446 is secured to the generally annular, interior surface 452 of thetransmission housing 454. The rotor 456 of the first motor/generator 446is secured to the inner, sun gear 424 of the first planetary gear set420.

The ring gear 434 of the second planetary gear set 432 may beselectively grounded to the housing 454, as by a first torque transferdevice 462 (C1). That is, the grounded ring gear 434 is selectivelysecured against rotation by an operative connection to the non-rotatablehousing 454. The ring gear 434 of the second planetary gear set 432 isalso selectively connected to the sun gear member 424, as by a secondtorque transfer device 464 (C2).

The carrier 426 is selectively grounded to the transmission housing viathe torque transfer device 465 (C3). Also, the sun gear member 436 isselectively connected to the ring gear member 422 via the torquetransfer device 467 (C4A).

A fifth torque transfer device 469 (C5) selectively connects the carrier426 with the sun gear member 436. A sixth torque transfer device 471(C4B) selectively connects the sun gear member 424 with the sun gearmember 436.

The torque transfer devices 462,464, 465, 467, 469 and 471 arepreferably all dog clutches.

The stator 466 of the second motor/generator 448 is also secured to thegenerally annular, interior surface 452 of the transmission housing 454.The rotor 468 of the second motor/generator 448 is secured to the sungear member 436 of the planetary gear set 432.

The two planetary gear sets 420 and 432 as well as the twomotor/generators 446 and 448 may be coaxially oriented, as about theaxially disposed central shaft 442. This configuration assures that theoverall envelope—i.e., the circumferential dimension—of the transmission410 may be minimized.

The output drive member 470 of the transmission 410 is secured to thecarrier 440 of the second planetary gear set 432.

The chart of FIG. 9 illustrates clutching engagements for differentoperating conditions of the transmission of FIG. 8. These torquetransfer device engagements are similar to those described above withreference to FIG. 7, except the sixth fixed ratio (F6) has been added.In the sixth fixed ratio (F6), the clutches 464, 465 and 469 areengaged. All of the fixed ratio shifts are single-transition shifts.

A seventh fixed ratio is available in this design, but it requiresdouble-transition shifts and is therefore impractical.

Conclusion

Each embodiment of the invention provides electrically variabletransmission, including an input member to receive power from an engine;an output member; first and second planetary gear sets each havingfirst, second and third gear members; first and second electricmotor/generators connected to members of the planetary gear sets; and atleast five selective torque transfer devices also connected to membersof the planetary gear sets. The torque transfer devices are selectivelyengageable in combinations of two or three to provide five or sixavailable fixed speed ratios, and, sequentially, an input-split mode, acompound-split mode, and an output-split mode, as output speed of thetransmission increases.

While only four preferred embodiments of the present invention aredisclosed, it is to be understood that the concepts of the presentinvention are susceptible to numerous changes apparent to one skilled inthe art. Therefore, the scope of the present invention is not to belimited to the details shown and described but is intended to includeall variations and modifications which come within the scope of theappended claims.

In the claims, the language “continuously connected” refers to a directconnection or a proportionally geared connection, such as gearing to anoffset axis.

1. An electrically variable transmission, comprising: an input member toreceive power from an engine; an output member; first and secondplanetary gear sets each having first, second and third gear members;first and second electric motor/generators connected to members of saidplanetary gear sets; five selective torque transfer devices alsoconnected to members of said planetary gear sets; wherein said torquetransfer devices are selectively engageable in combinations of two orthree to provide, sequentially, an input-split mode, a compound-splitmode, and an output-split mode, as output speed of the transmissionincreases, and to provide six available fixed speed ratios.
 2. Anelectrically variable transmission comprising: an input member toreceive power from an engine; an output member; first and secondmotor/generators; first and second planetary gear sets each havingfirst, second and third gear members; said input member beingcontinuously connected to said first member of said first planetary gearset, and said output member being continuously connected to said firstmember of said second planetary gear set; said first motor/generatorbeing continuously connected to said second member of said firstplanetary gear set; said second motor/generator being continuouslyconnected with said third member of said second planetary gear set; afirst torque transfer device selectively grounding said second member ofsaid second planetary gear set; a second torque transfer deviceselectively connecting said second member of said second planetary gearset to said second member of said first planetary gear set; a thirdtorque transfer device selectively grounding said third member of saidfirst planetary gear set; a fourth torque transfer device selectivelyconnecting said first or second member of said first planetary gear setwith said third member of said second planetary gear set; and a fifthtorque transfer device selectively connecting said third member of saidfirst planetary gear set with said third member of said second planetarygear set; wherein said torque transfer devices are selectivelyengageable in combinations of two or three to provide at least fiveavailable fixed speed ratios.
 3. The electrically variable transmissionof claim 2, wherein said first, second and third members of said firstplanetary gear set comprise a ring gear, sun gear and carrier,respectively, and said first, second and third members of said secondplanetary gear set comprise a carrier, ring gear and sun gear,respectively.
 4. The electrically variable transmission of claim 3,wherein said first planetary gear set is a compound planetary gear set,and said second planetary gear set is a simple planetary gear set. 5.The electrically variable transmission of claim 2, wherein a first fixedspeed ratio is achieved with the engagement of said first, fourth andfifth torque transfer devices; a second fixed speed ratio is achievedwith the engagement of said first, second and fifth torque transferdevices; a third fixed speed ratio is achieved with the engagement ofsaid first, third and fourth torque transfer devices; a fourth fixedspeed ratio is achieved with the engagement of said second, fourth andfifth torque transfer devices; a fifth fixed speed ratio is achievedwith the engagement of said second, third and fifth torque transferdevices; and a sixth fixed speed ratio is achieved with the engagementof said second, third and fourth torque transfer devices.
 6. Theelectrically variable transmission of claim 2, wherein a first fixedspeed ratio is achieved with the engagement of said first, fourth andfifth torque transfer devices; a second fixed speed ratio is achievedwith the engagement of said first, second and fifth torque transferdevices; a third fixed speed ratio is achieved with the engagement ofsaid second, fourth and fifth torque transfer devices; a fourth fixedspeed ratio is achieved with the engagement of said second, third andfifth torque transfer devices; and a fifth fixed speed ratio is achievedwith the engagement of said second, third and fourth torque transferdevices.
 7. The electrically variable transmission of claim 2, wherein afirst fixed speed ratio is achieved with the engagement of said first,fourth and fifth torque transfer devices; a second fixed speed ratio isachieved with the engagement of said first, second and fifth torquetransfer devices; a third fixed speed ratio is achieved with theengagement of said second, fourth and fifth torque transfer devices; afourth fixed speed ratio is achieved with the engagement of said second,third and fifth torque transfer devices; a fifth fixed speed ratio isachieved with the engagement of said second, third and fourth torquetransfer devices; and a sixth fixed speed ratio is achieved with theengagement of said second, third and sixth torque transfer devices. 8.An electrically variable transmission comprising: an input member toreceive power from an engine; an output member; first and secondmotor/generators; first and second planetary gear sets each havingfirst, second and third gear members; said input member beingcontinuously connected to said first member of said first planetary gearset, and said output member being continuously connected to said firstmember of said second planetary gear set; said first motor/generatorbeing continuously connected to said second member of said firstplanetary gear set; said second motor/generator being continuouslyconnected with said third member of said second planetary gear set; afirst torque transfer device selectively grounding said second member ofsaid second planetary gear set; a second torque transfer deviceselectively connecting said second member of said second planetary gearset to said second member of said first planetary gear set; a thirdtorque transfer device selectively grounding said third member of saidfirst planetary gear set; a fourth torque transfer device selectivelyconnecting said second member of said first planetary gear set with saidthird member of said second planetary gear set; and a fifth torquetransfer device selectively connecting said third member of said firstplanetary gear set with said third member of said second planetary gearset; wherein said torque transfer devices are selectively engageable incombinations of two or three to provide six available fixed speedratios.
 9. The electrically variable transmission of claim 8, whereinsaid first, second and third members of said first planetary gear setcomprise a ring gear, sun gear and carrier, respectively, and saidfirst, second and third members of said second planetary gear setcomprise a carrier, ring gear and sun gear, respectively.
 10. Theelectrically variable transmission of claim 8, wherein said firstplanetary gear set is a compound planetary gear set, and said secondplanetary gear set is a simple planetary gear set.
 11. The electricallyvariable transmission of claim 8, wherein a first fixed speed ratio isachieved with the engagement of said first, fourth and fifth torquetransfer devices; a second fixed speed ratio is achieved with theengagement of said first, second and fifth torque transfer devices; athird fixed speed ratio is achieved with the engagement of said first,third and fourth torque transfer devices; a fourth fixed speed ratio isachieved with the engagement of said second, fourth and fifth torquetransfer devices; a fifth fixed speed ratio is achieved with theengagement of said second, third and fifth torque transfer devices; anda sixth fixed speed ratio is achieved with the engagement of saidsecond, third and fourth torque transfer devices.
 12. The electricallyvariable transmission of claim 8, wherein a first fixed speed ratio isachieved with the engagement of said first, fourth and fifth torquetransfer devices; a second fixed speed ratio is achieved with theengagement of said first, second and fifth torque transfer devices; athird fixed speed ratio is achieved with the engagement of said second,fourth and fifth torque transfer devices; a fourth fixed speed ratio isachieved with the engagement of said second, third and fifth torquetransfer devices; a fifth fixed speed ratio is achieved with theengagement of said second, third and fourth torque transfer devices; anda sixth fixed speed ratio is achieved with the engagement of saidsecond, third and sixth torque transfer devices.
 13. The electricallyvariable transmission of claim 8, further comprising a sixth torquetransfer device selectively connecting said third member of said secondplanetary gear set with said first member of said first planetary gearset.